Spasticus is an alternative way of calling someone a Spaz, Retard, or Fuck Face. The word orginates from a song by 'Ian Dury and the Blockheads' in which the lyrics largely consist of : "I'm spasticus, I'm spasticus
I'm spasticus autisticus"

The main bonus that you get with the word 'Spasticus' is that you can spontaeneously burst into song.. singing the 'Spasticus Autisticus' song, and relatively few people find it as offensive as just calling someone a retard straight off.